1. Field of the Invention
The invention is generally in the field of hydraulic cement and concrete.
2. Relevant Technology
Supplementary Cementitious Materials (“SCMs”), such as fly ash, slag, natural pozzolans, and limestone, are often used to replace a portion of Portland cement in concrete. SCMs can yield improved concrete with higher durability, lower chloride permeability, reduced creep, increased resistance to chemical attack, lower cost, and reduced environmental impact. Reactive SCMs such as pozzolans react with calcium hydroxide released during cement hydration. Non-reactive SCMs such as limestone can serve as nucleation sites and/or as a filler to reduce water demand.
Portland cement, sometimes referred to as “cement clinker” or “OPC” (acronym for “ordinary Portland cement”), is the most expensive component of concrete. The manufacture of cement clinker contributes an estimated 5-7% of all manmade CO2. There is a long-felt but unmet need to reduce cement clinker (or “clinker”) consumption. There have been numerous academic conferences and publications dedicated to the concept of substituting a portion of clinker with SCM. Despite an oversupply of low cost SCMs, the industry has failed to overcome technical hurdles to more effectively utilizing SCMs. This failure, after years of research and discussion, to fully utilize readily available and less expensive waste SCMs to reduce clinker consumption, even though doing so would reduce cost and benefit the environment, shows that conventional practices for utilizing SCMs are inadequate.
Cement manufacturers almost universally produce OPC having a relatively broad particle size distribution (“PSD”) (e.g., between about 1-60 μm) and a particular chemistry in an attempt to strike a balance between the competing effects and demands of reactivity, rate of strength development, water demand, inter particle spacing, paste density, porosity and autogenous shrinkage. Cement manufacturers optimize OPC for use with itself, without regard to how OPC behaves when blended with SCMs.
SMCs are considerably less reactive than clinker and therefore delay set times and retard strength development by dilution. Although OPC-SMC blends can approach the strength of 100% OPC at later ages (>56 days), early (1-7 day) strength can be severely impacted when more than about 10-20% of OPC is replaced with SCM. Retardation of strength development and delays in set time limit SCM usage in concrete and are the reason why millions of tons of SCMs remain unused. The conventional solution is to “fix” SCMs to make them more reactive, e.g., by intergrinding with OPC or independently grinding them more finely than OPC. Neither “solution” has solved the problem of SCM underutilization.